Furnace control system



Nov. 29, 1938. J, |=i KRlECHBAUM 2,138,791

FURNACE CONTROL SYSTEM Filed Deo. 2, 1955 (jme/who@ www v Patented Nov. 29, 1938 UNITED STATES PATENT IOFFICE FURNACE CONTROL SYSTEM of Delaware Application December 2, 1935, Serial No. 52,466

10 Claims.

My invention relates to a furnace control system and more particularly to an arrangement employing a damper motor for actuating the dampers of the furnace.

In systems fo-r the automatic control of furnaces it is common to employ a damper motor for actuating the dampers, which damper motor is under the control of a. room thermostat. In such systems the dampers are usually moved from a position wherein the check damper is open and the draft damper is closed, to a position in which the opposite situation exists, depending upon whether the temperature in the room or other space to be heated is above or below the desired value. In ring a furnace, it is sometimes desirable that both the check and draft dempers be closed to prevent smoke from being forced out of the firing door during the firing operation. Since a thermostat is usually located in an upper room at some point remote from the furnace, it is common to provide a manual switch located on the damper motor or in proximity to the furnace, which switch upon being actuated causes -the damper motor to move the dampers to a position suitable for firing. The disadvantage of such devices, however, is that the operator often neglects to move the switch back to its normal position with the result that the furnace is no longer under automatic control. This is apt to lead to a situation wherein the temperature becomes excessive and in the event that no one is in the building at the time a dangerously high temperature may result. i

An object of the present invention is to provide a furnace control system embodying a damper motor having a basement switch in which provision is'made for automatically actuating the motor to a position wherein the check damper is open in the event that the temperature rises to an excessively high value by reason of the furnace being left in firing position.

A further object of the present invention is to provide a furnace control system employing a damper motor having a basement switch in which the damper motor is placed under the control of a suitable limit control upon the basement switch being closed.

Other objects of the invention will be apparent from the accompanying specification, claims and drawing.

In the single figure o-f my drawing, I have shown schematically my furnace control system. Referring to said figure, a. conventional hot air furnace is designated by theA reference numeral Thisl furnace is shown as having the usual hot air pipes.|2, a stack pipe I3, a fuel door I4, a draft damper l5 and a check damper I6. While I have shown the furnace as a hot air furnace it is to be understood that my invention is not to be so limited and the furnace may conveniently take any other conventional form.

'Ihe damper motor comprises a motor I 'l having a rotor |8 and a field winding I9. The motor is connected through reduction gearing 2|) with a shaft 2|. 'I'he shaft 2| is provided at its oppositeends with crank arms 22 and 23. Crank arm 22 is connected through a chain or equivalent device 24 with the draft damper and crank arm 23 is similarly connected through a chain 25 with the check damper. In the position shown, the draft damper is closed and the check damper is open. As will be obvious, continued rotation of shaft 2| causes successive opening and closing of draft damper "l5 and simultaneous closing and opening of check damper |6. Moreover, the length of the chains is such that a damper will not start to open until the crank arm to which it is connected has reached a horizontal position. Accordingly, when both crank arms are horizontal, both dampers are closed, which is the desirable condition for firing.

Mounted on the shaft 2| are three .cams 21, 28 and 29, which cams cooperate with switch arms 30, 3| and 32, respectively. Switch arms 30, 3| and 32 are adapted to be engaged with contacts 33, 35 and 36, respectively. The switch arms and the contacts constitute what may be termed a maintaining switch, the function of which will be apparent from the following description. Switch arms 30 and 3| are separated from their respective contacts by their associated cams at points 180 apart, whereas switch arm 32 is separated from its contact at a point half-way between the points at which switch arms 30 and 3| are separated from their contacts. Thus, if the position shown in the drawing may be considered as a starting point, switch arm 32 will be separated from contact 36 after 90 and 270 of rotation, while switch arm 3| will be separated after 180 of rotation and switch arm 30 after 360 of rotation.

Power for actuating the motor is supplied by a step-down transformer 38 having a line voltage 'primary 39 vand a low-voltage secondary .40. Primary 39 is connected to line wires .4| Aand 42.

The thermostat which controls the operation of the damper motor is designated generallyV byr the reference numeral 43. This thermostat is of the conventional form and comprises a bimetallic element 44 to which is attached a contact -arm 45.

Contact arm 45 is adapted to be engaged with either contact 46 o-r contact 47. The bimetallic element is so designed that upon the temperature dropping below the value desired the contact arm 45 will be moved into engagement with contact 46, while upon.- the temperature rising to the desired value the contact arm will be moved into engagement with vContact 41. Thus, contact 46 may be referred to as the cold contact and contact 41 as' the hot contact. While I have shown a room thermostat as the condition responsive switch, it will be understood that a switch responsive to any desired condition may be employed.

rIhe basement switch is designated by the reference numeral 48. This switch, which may take the form of any two-position switch adapted to be manually operated, is shown for purposes of illustration as comprising a switch arm 49 adapted to be moved into engagement with either contact v5|) or contact 5I In the normal position of the switch, switch arm 49 is in engagement with contact 5I, as shown in the drawing. With the switch in this position, the damper motor is under control of the thermostat 43.

A limit control is designated by the reference numeral 52. This limit control, which may take any conventional form, is shown for purposes of illustration as comprising a mercury switch 53 adapted to be actuated by a temperature responsive element consisting of a bulb 54 located at a suitable position, such as in the hot air pipe of the furnace, which bulb is connected through tubing' 55 with an expansible and contractible bellows 56. The bulb, tubing and bellows assemblage is iilled with a uid which expands and contracts with changes of temperature. The bellows bears against a pivoted support for .the mercury switch so that upon expansion of the bellows under a rise in temperature the leftend of the switch is tilted upwardly and upon a contraction of the bellows the left end is tilted downward. The mercury switch 53 is shown as comprising two pairs of contacts. The pair of contacts which comprises contacts 51 and 58 are shown as bridged by a pool of mercury 59. This is the position which the limit control assumes when the temperature is below the upper limit and, accordingly, these contacts may be designated as the cold contacts. 'Ihe other pair of contacts 60 and 6I are bridged by the mercury upon the tem' perature rising above the upper limit and, accordingly, may be referred -to as the hot contacts.

While the limit control is shown as a temperature responsive device, it is to be understood that it is not to be so limited. Thus, in the case of steam heat, a switch responsive to the steam pressure can be employed.

In the position shown in the drawing, the draft damper I5 is closed and the check damper I6 is open, as previously stated. Under these conditions, the draft is being retarded by reason of the check damper I6 being open and the furnace is being operated so as to generate as little heat as possible. Under these conditions, the room temperature will eventually fall below the desired value with the result that contact blade 45 is moved into engagement with the cold contact 46. This will cause the following circuit to be established through the ield winding. I9 of motor II1: From secondary 40, through conductors 62,

63 and 64, contact 5I, switch arm I49, conductors 65, 66 and 61, contact,35, switch arm 3|, conductor 68, conductor 69, bimetallic element 44, contact arm 45, contact 46, conductor 10, conductor lll, contact 56, mercury 59, contact 51, conductor 12, conductor 13, field winding I9 and conductor i4 to the other terminal of secondary 4B. lIll'he establishment of the circuit just traced causes 4the motor to be energized with the result that shaft ZI is rotated in the direction of the arrow it). After a very slight initial rotation of the shaft 2 I switch arm 3U will move into engagement with contact 33 so that the following maintaining circuit is established for the motor: From one end of secondary 40, through conductors 62, 53 and 64, contact 5I, switch arm 49, conductors 65, 66 and 61, contact .35, switch arm 3I, conductors 68 and 15, switch arm 30, contact 33, conductor 16, conductor 13, field windings I9 and conductor 'I4 back to the other terminal of secondary 46. It will be noted that the circuit just traced does not depend upon engagement of the thermostat contact arm 45 with contact 46 so that in the event that the contact arm is moved out of engagement with contact 46 shortly after the motor is starting on its cycle of operation there will be no danger of the motor stopping in some intermediate position.

The rotation of the motor will continue until switch arm 3l is moved out of engagement with contact 35 upon being engaged by the projection of cam 23 after'l80 of rotation. The moving of switch arm 3l out of engagement with contact 35 will interrupt both of the previously traced circuits so that the motor will be stopped. In the new position of shaft 2l the check damper i6 will be closed and the draft'damper I5 opened.

The motor will not again be actuated until the temperature rises sufliciently so that contact arm 45 is moved into engagement with'the hot contact 41. Upon this action-taking place, the following circuit will be established through eld winding I9: From secondary 40, through conductors 62, 63 and 64, contact 5I, switch arm 49, conductors 65, 66 and 11, contact 41, switch arm 45, bimetallic element 44, conductor 69, conduc tor 15, switch arm 30, contact 33, conductor 16, conductor 13, field winding I9 and conductor 14 back to the other terminal of the secondary 40. Upon the motor thus being energized, the motor will rotate in the direction of the arrow |00 as previously stated so that switch arm 3| is allowed to move back into engagement with contact 35 and a maintaining circuit will be established, which circuit is the same as the maintaining circuit traced during the previous half cycle of operation. The motor will continue to rotate until switch arm 30 is moved out of engagement with contact 33 as shown in the drawing. IInthe new position, the parts will again occupy the position shown in the drawing.

'Ihe operation of the basement switch will now be described. When itis desired to move the dampers to a firing position, the basement switch arm 49 is moved into engagement with contact 50. Upon this being done, both the dampers will be moved to a closed position regardless of the position which they are in at the time switch 48 is actuated. The operation of the motor, which will result upon this movement of switch 48, will first be' described, when the switch' is engaged' arm 49, contact 50, conductor 80, conductor 1I, 75

contact 58, mercury 59, contact 51, conductor 12, conductor 13, field winding I9, and conductor 14 to the other terminal of the secondary 46. It will be noted that this circuit does not include either switch arm 36 or 3|. Accordingly, the engagement of switch arm 49 with contact 50 will result in this circuit being established regardless of the position of the damper motor. The establishment of this circuit causes the motor to rotate shaft 2 I. This rotation will continue for 90 until switch arm 32 is moved out of engagement with contact 36 by reason of the switch arm being engaged with one of the toes of cam 29. This will cause the circuit to the motor to be interrupted. Regardless of whether the rotation is initiated when the dampers are in the position shown or in the opposite position, the 90 rotation of the shaft will result in a new position of the shaft 2| in which the crank arms 22 and 23 are horizontal and both dampers I5 and I6 are closed.

This position is the most desirable position for firing. After the operator has completed his firing operation he should turn the switch arm 49 back into engagement with contact 5I, whereupon the motor will be rotated, since switch arms 36 and 3I are in engagement with contacts 33 and 35, respectively, to a position wherein it is again under control of the room thermostat, which will occur when the toe of either cam 21 or 28, depending upon the position of the mechanism, separates its associated switch arm from the adjacent contact.

In the event, however, that the operator fails to move the basement switch 48 back to the normal position the system is designed to prevent any danger of the furnace becoming over-heated,

as previously set forth. Upon the temperature of the furnace reaching a predetermined value, the bellows 56 will be sufficiently expanded to move the mercury switch into a position wherein the mercury 59 is in engagement with contacts 66 and 6I. Upon this taking place, the following circuit is established through the motor: From secondary 4U, through conductors 62, 63, 8|, contact 6I, mercury 59, contact 60, conductors 82, 68 and 15, switch 30, contact 33, conductor 16, conductor 13, field winding I9 and conductor 14 to the other terminal of the secondary 40. This movement of the motor will continue until switch arm 36 is disengaged from contact 33. When this takes place, the shaft 2I will be in the position shown in the drawing wherein the check draft I6 is open. This damper position will be maintained until the furnace temperature cools down suiiiciently that the mercury 59 is moved out of engagement with contacts 60 and 6I and into a position where it again bridges contacts 51 and 58. This will re-establish the circuit rst traced in connection with the moving of switch arm 49 into engagement with contact 56 so that the dampers are again run to a mid-position wherein both of them are closed. This action will continue until the occupant of the dwelling either discovers that the basement switch is in the firing position or becomes aware of the fact through the temperature of the room rising excessively. At the same time, there is no danger of the furnace temperature becoming so excessive as to create a dangerous situation.

While I have described the operation of the limit control in connection with the situation which occurs when the basement switch 48 is inadvertently left in firing position, this is not the only time that the limit control will function.

The limit control further operates in the usual manner to close the draft damper and open the check damper in the event that the furnace temperature becomes excessively hot when the dampers are in the usual draft producing condition; i. e. when the draft damper I5 is opened and the check damper I6 is closed. Under these conditions, the circuit established by reason of the limit switch being actuated to the position where mercury 59 is in engagement with contacts 66 and 6I will be the same as that previously traced. Thus, the limit switch serves to effectively prevent the temperature of the furnace reaching an excessive value whether the position of the damper is due to the thermostat or due to the basement switch being inadvertently left in firing position.

Moreover, inasmuch as the operation of the limit switch does not depend upon the position of the basement switch 48, the limit switch is operative even though the basement switch should inadvertently be left in intermediate position so that it is in engagement with neither contact 50 nor contact 5I. If the basement switch is inadvertently left in this position and the dampers are not already in mid position they will be moved into mid position upon the contact arm 45 moving into engagement with either contact 46 or 41. The circuit through the field winding in this case extends from conductor 62, through switch arm 32, contact 36 and conductor 19 to the conductor 66. The circuit is otherwise the same as previously traced in connection with ,the operation of the motor by the thermostat 43.

Since switch arm 32 is moved away from contact 36 whenv the shaft is in a position such that the arms 22 and 23 are horizontal, this circuit will be interrupted when the shaft is in such positions so that the dampers will be left in mid position. The limit switch then functions in the same manner as when the dampers have been placed in mid position by the normal operation of the basement switch. It will be noted that this connection between conductors 62 and 66, through switch arm 32 and contact 36 plays no part in the operation of the motor so long as switch arm 49 is in engagement with contact 5I. When switch arm 59 is in this position, switch arm 32 and contact 36 are bridged by the parallel circuit including conductors 63 and 64, lcontact 5I, switch arm 49 and conductor 65.

It will be seen that I have provided a relatively simple damped control system employing a damper motor with a baseemnt switch, in which there is an assurance that the temperature of the furnace will not rise excessively in the event that the basement switch is inadvertently left in firing position. It will further be seen that if the basement switch is left in firing position the furnace will go under control of the limit control so that the temperature will neither rise excessively or will be allowed to drop to a value in which there is danger of the fire being extinguished.

While I have disclosed a specific embodiment of my invention, it will be understood that this is for purposes of illustration only and that my invention is to be limited only by the scope of the appended claims.

I claim as my invention:

1. In combination, a furnace, a damper means therefor movable between draft retarding and draft producing positions, motor means for moving said damper means, means for normally operating said motor so as to move said damper said space, and further means for controlling said motor in accordance with a furnace condition to cause said motor to move said dampers to the draft retarding position from said intermediateposition upon said furnace condition assuming a predetermined value.

2. In combination, a furnace, damper means therefor movable between draft retarding and draft producing positions, motor means for moving said damper means, means for normally operating said motor so as to move said damper means between said draft retarding and draft producing positions in accordance with a condition at one control point, manually operated means for varying the operation of said motor so as to move said damper means to an intermediate position regardless of the temperature of said space, and further means for controlling said motor in accordance with a furnace condition to `cause said motor to move said dampers to the draft retarding position from either said intermediate or draft producing position upon the furnace condition assuming a predetermined value.

3. In combination, a furnace, damper means therefor movable between draft retarding and draft producing positions, a motor, means for connecting said motor to said dampers so that continuous movement of said motor in the same direction produces successive movements ofsaid damper means between draft retarding and draft producing conditions, means for normally operating said motor so as to move said damper means between said draft retarding and draft producing positions in accordance with the value of a condition at one control point, manually operated means for varying the operation of said motor so as to move said damper means yto an interl mediate position regardless of the temperature of said space, and further means for controlling said motor in accordance with a condition at a furnace\control point to cause said motor to move said dampers to the draft retarding position from said intermediate position upon the condition at said furnace control point assuming a predetermined value.

4. In combination, a furnace, damper means therefor movable between draft retarding and draft producing positions, an electric motor, connections betweenl said motor and said damper means for causing movement of the latter by the former, a maintaining switch actuatedby said motor, a temperature responsive switch located in a space heated by said furnace, a source of electrical energy, connections between said motor and said source vof/electrical energy including said maintaining switch and said temperature responsive switch for causing said motor to be successively energized to move said damper means between said draft retarding and draft producing positions, further connections between said motor and source `of energy including said maintaining switch and a manual switch for causing said motor to move'said damper means to an intermediate ring position regardless of the position of said temperature responsive switch, a furnace condition responsive switch and connections between said motor and said source of energy including said maintaining switch and said furnace condition responsive switch operative upon the condition to which it is responsive assuming a predetermined value to cause the motor to move said damper means to the draft retarding position from either a draft producing position or from said intermediate position.

5. In combination, a furnace, draft and check dampers therefor, motor means for moving said damper means, means for normally operating said motor so as to move said dampers in accordance with the temperature of a space heated by said furnace between a draft retarding position in which the draft damper is closed and the check damper open and a draft producing positionin which the draft damper is open and the check damper closed, manually controlled means for varying the operation of said motor so as to move said dampers to an intermediate position in which they are both closed regardless of the temperature of said space, and further means for controlling said motor in accordance with a furnace condition to cause said motor means to move said dampers to the draft retarding position from said intermediate position upon said furnace condition assuming a predetermined value.

6. In combination, a furnace, damper means therefor movable between draft retarding and draft producing positions, an electric motor, connections between said motor and said damper means for causing movement of the latter b y the former, a temperature responsive switch located in a space heated by said furnace, a source of electrical energy, connections between said motor and said source of electrical energy including said temperature responsive switch for causing said motor to be successively energized to move said damper means between said draft retarding and draft producing positions, further connections between said motor and source of energy including a manual switch for causing said motor to move said damper means to a desired firing position regardless of the position of said temperature responsive switch, a furnace condition responsive switch, and connections between said motor and said source of energy including said furnace condition responsive switch operative upon the condition to which it is responsive assuming a predetermined value to cause the motor to move said damper means to the draft retarding position from said firing position.

7. In combination, a furnace, dampermeans therefor movable between draft retarding and draft producing positions, an electric motor, connections between said motor and said damper means for causing movement of the latter by the former, a condition responsive switch, a source of electrical energy, connections between said motor and said source of electrical energy including said condition responsive switch for causing said motor to be successively energized to move said damper means between said draft retarding and draft producing positions, further connections between said motor and source of energy including a manual switch for causing said motor to move said damper means to a. desired firing position regardless of the position of .said condition responsive switch, a furnace condition responsive switch, and lconnections between said motor and said source of energy including said furnace condition responsive switch operative upon the condition to which itis responsive assuming a predetermined value to cause the motor to move said damper means to the draft retarding position from said firing position.

8. In combination, a furnace, damper means therefor movable between draft retarding and draft producing positions, motor means for moving said damper means, connecting means between said motor and said damper means effective i,on successive half cycles of movement produced by rotation of the motor in the same direction to cause movement of the dampers to said draft retarding and said draft producing position, a temperature responsive switch movable between hot and cold positions, first, second and third normally closed cycling switches, means for opening said first cycling switch when said damper means is in its draft retarding position, said second cycling switch when said damper means is in its draft producing position, and said third cycling switch when said damper means is in a predetermined intermediate position, a manual switch movable between automatic and manual positions, a source of power, connections between said source of power, said temperature responsive switch, said motor, said first and second cycling switches, and 'said manual switch such that when said manual switch is in its automatic position, said damper means is in its draft retarding position, and said temperature responsive switch moves to its cold position, said motor is energized to move said damper means to its draft producing v position, the opening of said second cycling switch terminating the operation of said motor, and that when subsequently said temperature responsive switch is moved to its hot position, said damper means is moved to its draft retarding position, the

' opening of said first cycling switch terminating the operation of said motor, said connections including a connection between said motor and its source of power independent of said temperature `responsive switch and including said rst and second cycling switches connected in series and said manual switch when in its automatic position so that said cycling switches singly function to terminate the operation of the motor at the end of each half cycle and jointly function to maintain the operation of the motor independently of the temperature responsive switch whenever the damper means is in any intermediate position, and further connections between said motor, said source of power, said manual switch and said third cycling switch effective when said manual switch is moved to the manual position to place said motor under the control of said third cycling switch independently of said first and second cycling switches and said thermostat.

9. In combination, a furnace, damper means therefor movable between draft retarding and draft producing positions, motor means for moving said damper means, connecting means between said motor and said damper means effective on successive half cycles of movement produced by rotation of the motor in the same direction to cause movement of the dampers to said draft retarding and said draft producing positions, `a temperature responsive switch-movable between hot and cold positions, first, second, and third normally closed cycling switches, means for opening said first cycling switch when said damper means is in its draft retarding position, said second cycling switch when said damper means is in its draft producing position, and said third cycling switch when said damper means is in a predetermined intermediate position, a manual switch movable between automatic and manual positions, a source of power, connections between said source of power, said temperature responsive switch, said motor, said first and second cycling switches, and said manual switch such that when said manual switch is in its automatic position, said damper means is in its draft retarding position, and said temperature responsive switch moves to its cold position, said motor is energized to move. said damper means to its draft producing position, the opening of said second cycling switch terminating the operation of said motor, and that when subsequently said temperature responsive switch is moved to its hot position, said damper means is moved to its draft retarding position, the opening of said first cycling switch terminating the operation of said motor, said connections including a connection between said motor and its source of power independent of said temperature responsive switch and including said first and second cycling switches connected in series and said manual switch when in its automatic position so that said cycling switches singly function to terminate the operation of the motor at the end of each half cycle and jointly function to maintain the operation of the motor independently of the temperature responsive switch whenever the damper means is in any intermediate position, further connections between said motor, said. source of power, said manual switch and said third cycling switch effective when saidmanual switch is moved to the manual position to place said motor under the control of said third cycling switch and independent of said first and second cycling switches and said thermostat, a limit switch responsive to a limiting condition, and connections between said limit switch, said motor, and said previously named circuit whereby when said condition is above a predetermined value, and said damper means is in any position other than draft retarding position, said motor is energized to move said dampers to draft retarding position, regardless of the position of said basement switch. v

10. In combination, a furnace, damper means therefor movable between draft retarding and draft producing positions, an electric motor, connections between said motor and said damper means for causing movement of the latter by the former, a source of electrical energy, a condition responsive switch, a manual switch movable between two circuit controlling positions, connec- -tions between said motor, said source of electrical energy, said condition responsive switch, and said manual switch operative upon said manual switch being in one circuit controlling position to place said motor under the control of said condition responsive switch and upon said manual switch being in the other circuit controlling position to operate said `motor independently of said condition responsive switch to a position intermediate of the said draft vretarding and draft producing positions, a furnace condition responsive switch, and connections between said motor, said furnace condition responsive switch, and said source of electrical energy to operate said motor so as to move said dampers to a draft retarding position upon the furnace condition assuming a predeter- Ymined value, saidlast named connections being JOHN P. KRIECHBAUM. 

